1. Field of the Invention
This invention relates to a network component, particularly to an Ethernet switch and its method of switching, for selectively transmitting data among several data ports or filtering network packets.
2. Description of the Prior Art
Ethernet is the most popular local area network (LAN) in digital communication market. Previously, the Ethernet framework is a 10BASE5 bus topology network. 10BASE2 is a lower cost improvement of 10BASE5. Although 10BASE2 and 10BASE5 belong to the same bus topology network and operate at the same 10 Mhz frequency, 10BASE2 uses a different type of coaxial cable, and its transmission distance is limited to 200 meters. Both 10BASE5 and 10BASE2 networks have the following drawbacks: costly installation, inflexible installation, and inability to use existing wiring system in the building, among others. 10BASE-T network has been proposed to make use of twisted cable to construct a star topology network for overcoming the drawbacks of 10BASE2 and 10BASE5 network.
When the scale of LAN grows larger and the load of digital transmission among LANs is also increases, the Ethernet performance degrades with the increasing number of nodes connected the LANs. Consequently, high speed Ethernet operating at high clock frequency is provided to address to the requirement for large-scale LANs or high speed digital terminals. High speed Ethernet operates at 100 MHz clock frequency to basically improve the performance of the 10BASE Ethernet. Moreover, high speed Ethernet also defines a media independent interface, for easy connection of said network nodes to twisted cable media or fiber optical media-based networks, such as 100BASE-TX, 100BASE-T4, or 100BASE-FX networks.
Basically, 10BASE5, 10BASE2, 10BASE-T, 100BASE-TX, 100BASE-T4 or 100BASE-FX belong to the shared network system. That is, the bandwidth of the entire network system is shared by all nodes in the interconnecting network system. The bandwidth for 10BASE network system is 10 MHz, and the bandwidth for 100BASE is 100 MHz. Consequently, when the number of nodes in the interconnecting network system exceeds a critical value, the performance of said network system becomes saturated. To overcome this problem, segmenting methodology is employed to segment the entire network system into several independent sub-networks and place each sub-network in a different collision domain. Therefore, nodes connecting to a different sub-network do not share the bandwidth of other sub-networks. For example, if a non-segmented shared 100BASE network system connects 100 nodes, then each node of the fully loaded network shares only 1 MHz bandwidth. In contrast, if said shared 100BASE LAN system is segmented into two segments, then each node of the fully loaded network shares 2 MHz bandwidth. The segmented LAN employing the Ethernet protocol is called a switching Ethernet. Transmitted packets in different segments are switched by the Ethernet switch. The main purpose of the Ethernet switch is to switch the packets to different segments of the LAN; therefore, packets from one segment are delivered to another segment, while packets from a node to another node in the same segment are not delivered.
Associated technology is disclosed in U.S. Pat. Nos. 5,274,631 and 5,491,694.
FIG. 1 is a block diagram illustrating the circuit of the discrete memory structure of the Ethernet switch.
As shown in FIG. 1, the Ethernet switch basically comprises of switch integrated circuit 100 and several port integrated circuits 110a, 110b, and 110c. The switch integrated circuit 100 controls the delivery and switch of network packets among ports. Port integrated circuits 110a, 110b, and 110c comprise internal memories 120a, 120b, and 120c for saving and switching network packets. Under this Ethernet framework, when a network packet is to be transmitted from port 130a to port 130b, the packet has to be first saved in the memory 120a, then transported from the memory 120a to the memory 120c. Therefore, the operating performance of this Ethernet switch is not promising. In addition, to enable the links of various LANs, such as 100BASE5, 10BASE2, 10BASE-T, 100BASE-TX, 100BASE-T4, or 100BASE-FX this type of Ethernet switch requires external memory, which is an additional cost.